The United States and Japan will step up their defence cooperation to deal with the threat from nuclear-armed North Korea as tensions in East Asia remain high, officials from the two allies said on Thursday.

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The men were released pending further inquiries, with the three now charged.

It is unclear what has happened to the fourth man.

The charges against Landeryou swing attention to his partner, Senator Kitching, who was controversially selected in October to fill the Victorian senate seat left empty by Labor powerbroker Stephen Conroy.

Senator Kitching, a lawyer and former HSU official, was chosen by Labor's public office selection committee amid intense speculation she was also the captain's pick of her long-time friend, Mr Shorten.

Her endorsement reportedly sparked unease among many Labor members and afforded the Liberals a wealth of opportunities for union jibes.

The Liberals were quick to point out she had been hauled before the Royal Commission into Trade Union Governance and Corruption and chastised over official workplace tests.

On Thursday, Labor's human services spokesman, Doug Cameron, said anyone trashing Australia's democratic processes should face the full force of the law - no matter who they were.

"If people are vandalising signs, if people are trashing the democratic processes, and it's illegal to do that, they should be dealt with under the law. Full stop, no argument," the senator told reporters in Sydney.

"It's not an issue of who they've got links to, this is an issue that's before the courts ... they will be dealt with, and Labor has got no tolerance for the democratic processes being trashed."

Special Minister of State Scott Ryan shied away from commenting when talking to reporters in Melbourne about issues of the day on behalf of the Turnbull government.

He said it was "probably not appropriate for me to make public comment until after the court matters have concluded".